Microstructure and Hardness of Hollow Tube Shells at Piercing in Two-High Screw Rolling Mill with Different Plugs

Abstract

AA6060 ingots were pierced in a two-high screw rolling mill (MISIS-130D) with guiding shoes (Mannesmann mill type). Three different plugs, i.e., a conventional entire plug, a plug with a cavity, and a hollow plug, were used for piercing. We established that the grain size decreases after piercing, by order of magnitude, compared to the initial non-pierced annealed bill, with a grain size of 100–400 μm, and the hollow shell grains are elongated along the piercing direction. The produced hollow shells had 30% higher hardness than the initial billet. The highest hardness values were obtained after piercing the conventional entire plug. The most uniform hardness distribution through the hollow shell’s volume was obtained after piercing the hollow plug. The cross and longitudinal section hardness measurements demonstrate that the hardness decreases from the outer surface to the inner surface of the hollow shells.

Microstructural and Mechanical Analysis of Seamless Pipes Made of Superaustenitic Stainless Steel Using Cross-Roll Piercing and Elongation

“…These phenomena also contribute significantly to the formation of a certain grain structure and the required level of mechanical properties and, therefore, must be taken into account when developing the manufacturing process [12][13][14][15][16]. At the moment, a large number of studies have been carried out on the features of the stainless-steel tube piercing and rolling processes [17][18][19]. However, most of them have been aimed at studying the wear resistance of the tool, the accuracy of pipes, or the piercing parameters to be selected [20][21][22].…”